JP2020129434A - Aging method of fuel cell - Google Patents

Abstract

To provide an aging method of fuel cell capable of shortening the aging time, while restraining deviation of current distribution across the cells.SOLUTION: In an aging method of fuel cell, power generation currents near a fuel gas inlet 31 and an oxidant gas inlet 32, and near a fuel gas outlet 34 and an oxidant gas outlet 35 are measured respectively. When the measured values of power generation currents near the fuel gas inlet 31 and the oxidant gas inlet 32 are larger than the measured values of power generation currents at the fuel gas outlet 34 and the oxidant gas outlet 32, humidity of fuel-gas and oxidant gas to be humidified is lowered, and when the measured values of power generation currents near the fuel gas inlet 31 and the oxidant gas inlet 32 are smaller than the measured values of power generation currents near the fuel gas outlet 34 and the oxidant gas outlet 32, humidity of the fuel-gas and oxidant gas to be humidified is increased.SELECTED DRAWING: Figure 4

Description

The present invention relates to a fuel cell aging method.

A fuel cell (also referred to as a fuel cell stack) is formed by stacking a plurality of cells, and supplies fuel gas (for example, hydrogen) and oxidant gas (for example, air) that are reaction gases to an anode electrode and a cathode electrode. It is a system that obtains electric energy (electromotive force) by electrochemically reacting with each other.

A cell of a fuel cell (also referred to as a fuel cell or a single cell) comprises an ion-permeable electrolyte membrane, and an anode-side catalyst layer (electrode layer) and a cathode-side catalyst layer (electrode layer) that sandwich the electrolyte membrane. It has a membrane electrode assembly (MEA: Membrane Electrode Assembly). Gas diffusion layers (GDL: Gas Diffusion Layer) are formed on both sides of the MEA for supplying a fuel gas or an oxidant gas and collecting electricity generated by an electrochemical reaction. The MEA in which the GDLs are arranged on both sides is called MEGA (Membrane Electrode & Gas Diffusion Layer Assembly), and the MEGA is sandwiched by a pair of separators. Here, MEGA is the power generation unit of the fuel cell (that is, the power generation unit of the cell), and when there is no gas diffusion layer, MEA is the power generation unit of the fuel cell.

In this type of fuel cell, the initial power generation performance is low due to the resistance of the initial dry electrolyte membrane, the oxide film formed on the catalyst in the manufacturing process, and the poisoning of the catalyst by volatile organic substances. Therefore, in order to bring out desired power generation performance after the fuel cell is assembled, a preparatory operation (leveling operation) called a fuel cell aging operation (sometimes simply referred to as aging) is performed. In this aging operation, by preliminarily generating electric power after the fuel cell is assembled, the electrolyte membrane is wetted to reduce the resistance of the electrolyte membrane (in other words, the conductivity of the electrolyte membrane is increased), and the oxide film on the catalyst surface is formed. By removing the organic substances, the cell performance can be brought to a desired level. In addition, not only after manufacturing, but when the power generation is restarted (e.g., after restarting) after the fuel cell is shut down (particularly after being shut down for a long time), output characteristics such as electromotive force due to long-term power generation. The output characteristics of the fuel cell may be recovered by performing the above-mentioned aging operation even when the fuel cell is lowered.

However, the time (aging time) required for the aging (run-in operation) of the fuel cell as described above is very long, and it has become a major problem in the manufacturing process with the increase and spread of the number of production.

Therefore, in order to perform aging in a short time (in other words, shorten the aging time), various proposals have been conventionally made. For example, in Patent Document 1 below, by supplying a humidified reaction gas to a fuel cell and maintaining an electrolyte membrane in a good wet state, it is possible to suppress variations in cell activity and shorten the aging time. Is disclosed.

JP, 2013-069673, A

However, the above-described fuel cell aging method has the following problems. That is, as shown in FIG. 5B, when the humidified reaction gas flows through the cell, it enters the reaction gas passage from the reaction gas inlet of the cell and is discharged to the outside via the reaction gas outlet of the cell. Therefore, the electrolyte membrane near the reaction gas inlet is wetted by the water contained in the reaction gas, and the electrolyte membrane near the reaction gas outlet is wetted last. Here, the water contained in the reaction gas gradually decreases as it approaches the reaction gas outlet, but since water is generated by the electrochemical reaction, the wet state of the electrolyte membrane is maintained by the generated water.

In the case shown in FIG. 5B, since the electrochemical reaction is most active near the reaction gas inlet, a large amount of the reaction gas is consumed near the reaction gas inlet, and the reaction gas that can be consumed as the reaction gas approaches the outlet. Is getting smaller. As a result, the generated current gradually decreases from the reaction gas inlet toward the reaction gas outlet, that is, the current distribution in the entire cell is biased. When the current distribution is biased, a portion where aging progresses well and a portion where aging progresses poorly occur, which causes a problem that the aging time of the fuel cell becomes rather long.

The present invention has been made to solve such a technical problem, and an object of the present invention is to provide an aging method for a fuel cell capable of shortening the aging time while suppressing the bias of the current distribution of the entire cell. To do.

The fuel cell aging method according to the present invention is a fuel cell aging method of supplying a humidified reaction gas to perform aging for a fuel cell in which a plurality of cells having a reaction gas inlet and a reaction gas outlet are stacked. And at least the generated currents near the reaction gas inlet and the reaction gas outlet are measured, respectively, and the measured value of the generated current near the reaction gas inlet is larger than the measured value of the generated current near the reaction gas outlet. To lower the humidity of the reaction gas to be humidified, and if the measured value of the generated current near the reaction gas inlet is smaller than the measured value of the generated current near the reaction gas outlet, set the humidity of the humidified reaction gas to It is characterized by raising.

In the fuel cell aging method according to the present invention, the generated currents near the reaction gas inlet and the reaction gas outlet are measured, respectively, and the measured value of the generated current near the reaction gas inlet is smaller than the measured value of the generated current near the reaction gas outlet. If the measured value of the generated current near the reaction gas inlet is smaller than the measured value of the generated current near the reaction gas outlet, the humidity of the reaction gas to be humidified is increased. By doing so, it is possible to suppress the bias of the current distribution of the entire cell and keep the current distribution uniform. As a result, the aging time can be shortened.

According to the present invention, it is possible to reduce the aging time while suppressing the deviation of the current distribution of the entire cell.

(A) is a cross-sectional view of a main part of a fuel cell to which the aging method of a fuel cell is applied, and (B) is an overall external view of a fuel cell to which the aging method of a fuel cell is applied. It is a top view which shows the cell of a fuel cell. It is a figure for demonstrating the aging method of the fuel cell which concerns on embodiment. It is a flow figure showing the aging method of the fuel cell concerning an embodiment. (A) is an image diagram for explaining the wet state of the electrolyte membrane, the reaction gas concentration and the generated current in the present invention, and (B) shows the wet state of the electrolyte membrane, the reaction gas concentration and the generated current in the prior art. It is an image figure for explaining.

Hereinafter, an embodiment of a fuel cell aging method according to the present invention will be described with reference to the drawings. The "reaction gas" in the present embodiment refers to the fuel gas and the oxidant gas as described above, and when it is necessary to distinguish the two in the following description, "fuel gas" or "oxidant gas" "Reaction gas" when there is no need to distinguish.

[Structure of fuel cell]
First, a structure of a fuel cell to which the fuel cell aging method is applied will be briefly described with reference to FIGS. 1 and 2. FIG. 1A is a cross-sectional view of a main part of a fuel cell to which a fuel cell aging method is applied, and FIG. 1B is an overall external view of a fuel cell to which a fuel cell aging method is applied. .. FIG. 2 is a plan view showing a cell of a fuel cell.

As shown in FIG. 1(A), the fuel cell 10 has a plurality of stacked cells 1 as a basic unit. The cell 1 is a polymer electrolyte fuel cell that generates an electromotive force by an electrochemical reaction between an oxidant gas (for example, air) and a fuel gas (for example, hydrogen). The cell 1 includes a MEGA 2 and a separator 3 that contacts the MEGA 2 so as to partition the MEGA 2. As shown in FIG. 1A, the MEGA 2 is sandwiched by a pair of separators 3, 3.

The MEGA 2 is one in which the membrane electrode assembly (MEA) 4 and the gas diffusion layers 7, 7 arranged on both surfaces of the membrane electrode assembly 4 are integrated. The membrane electrode assembly 4 is composed of an electrolyte membrane 5 and a pair of electrodes 6 arranged so as to sandwich the electrolyte membrane 5. The electrolyte membrane 5 is made of a proton conductive ion exchange membrane made of a solid polymer material, and the electrode 6 is made of, for example, a porous carbon material carrying a catalyst such as platinum. The electrode 6 arranged on one side of the electrolyte membrane 5 serves as an anode, and the electrode 6 on the other side serves as a cathode. The gas diffusion layer 7 is formed of a conductive member having gas permeability such as a carbon porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or foam metal.

In the present embodiment, the MEGA 2 is the power generation unit of the fuel cell 10, and the separator 3 is in contact with the gas diffusion layer 7 of the MEGA 2. Moreover, when the gas diffusion layer 7 is omitted, the membrane electrode assembly 4 is a power generation part, and in this case, the separator 3 is in contact with the membrane electrode assembly 4. Therefore, the power generation section of the fuel cell 10 includes the membrane electrode assembly 4 and contacts the separator 3.

The separator 3 is a plate-shaped member whose base material is a metal having excellent conductivity and gas impermeability. One side of the separator 3 is in contact with the gas diffusion layer 7 of the MEGA 2 and the other side is adjacent to the other separator. 3 is in contact with the other surface side.

In this embodiment, each separator 3 is formed in a corrugated shape or an uneven shape. The shape of the separator 3 is such that the wave shape is an isosceles trapezoid, the wave top is flat, and both ends of this wave are equally angled. That is, each separator 3 has substantially the same shape when viewed from the front side and the back side. The top portion of the separator 3 is in surface contact with one gas diffusion layer 7 of the MEGA 2, and the top portion of the separator 3 is in surface contact with the other gas diffusion layer 7 of the MEGA 2.

A space defined between the gas diffusion layer 7 on one electrode (for example, anode) 6 side and the separator 3 serves as a fuel gas passage 21 through which the fuel gas flows, and the other electrode (for example, cathode). The space defined between the gas diffusion layer 7 on the 6 side and the separator 3 serves as an oxidant gas passage 22 through which the oxidant gas flows. When the fuel gas is supplied to the fuel gas flow path 21 facing the cell 1 via the cell 1 and the oxidant gas is supplied to the oxidant gas flow path 22, an electrochemical reaction occurs in the cell 1 to generate an electromotive force. , Water is produced (ie, produced water). Further, one end of the fuel gas flow path 21 communicates with a fuel gas inlet 31 described later, and the other end communicates with a fuel gas outlet 34. One end of the oxidant gas flow path 22 communicates with an oxidant gas inlet 32, which will be described later, and the other end communicates with an oxidant gas outlet 35.

The cells 1 having such a structure are stacked with the electrode 6 serving as the anode of a certain cell 1 and the electrode 6 serving as the cathode of another cell 1 adjacent thereto facing each other. In addition, a back-side top portion of the separator 3 arranged along the electrode 6 serving as an anode of a certain cell 1 and a back surface side of the separator 3 arranged along the electrode 6 serving as a cathode of another adjacent cell 1. The top is in surface contact. A space defined between the separators 3 and 3 that are in surface contact between two adjacent cells 1 serves as a cooling water passage 23 through which cooling water that cools the cells 1 flows. Further, one end of the cooling water flow path 23 communicates with a cooling water inlet 33, which will be described later, and the other end communicates with a cooling water outlet 36.

As shown in FIG. 2, a fuel gas inlet 31, an oxidant gas inlet 32, and a cooling water inlet 33 are sequentially arranged at one end (the left end in FIG. 2) in the longitudinal direction of the cell 1. .. A fuel gas outlet 34, an oxidant gas outlet 35, and a cooling water outlet 36 are sequentially arranged at the other end (the right end in FIG. 2) in the longitudinal direction of the cell 1. The fuel gas inlet 31 and the oxidant gas inlet 32 correspond to the "reaction gas inlet" in the claims, and the fuel gas outlet 34 and the oxidant gas outlet 35 correspond to the "reaction gas inlets" in the claims. It corresponds to the “reaction gas outlet”.

The fuel gas inlet 31 is connected to the fuel gas supply pipe 11a attached to the outside of the fuel cell 10, and the fuel gas outlet 34 is connected to the fuel gas exhaust pipe 11b (see FIG. 1B). The oxidant gas inlet 32 is connected to the oxidant gas supply pipe 12a attached to the outside of the fuel cell 10, and the oxidant gas outlet 35 is connected to the oxidant gas discharge pipe 12b. The cooling water inlet 33 is connected to the cooling water supply pipe 13a attached to the outside of the fuel cell 10, and the cooling water outlet 36 is connected to the cooling water discharge pipe 13b.

In addition, as shown in FIG. 2, the MEGA 2, the fuel gas inlet 31, the oxidant gas inlet 32, the cooling water inlet 33, the fuel gas outlet 34, the oxidant gas outlet 35, and the cooling water outlet 36 are provided in the peripheral portion of the cell 1. An annular gasket 8 is attached so as to surround the. The gasket 8 is made of rubber, thermoplastic elastomer, or the like, and seals a space between adjacent cells 1 when the cells 1 are stacked as an inter-cell seal member.

[Fuel cell aging method]
Hereinafter, the aging method of the fuel cell will be described with reference to FIGS. 3 and 4. The fuel cell aging method according to the present embodiment is a method of performing aging by supplying a humidified fuel gas and an oxidant gas to the above-described fuel cell 10 using the aging device 40 shown in FIG. 3, for example. ..

The aging device 40 includes a humidifier 41 attached to the fuel gas supply pipe 11a, a humidifier 42 attached to the oxidant gas supply pipe 12a, a current near the fuel gas inlet 31 and the oxidant gas inlet 32 in the cell 1. Is provided with a current measuring device 43 that measures the current, a current measuring device 44 that measures the current in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35, and a control unit 45 that controls the entire aging device 40.

The humidifiers 41, 42 are, for example, bubblers that humidify the reaction gas through water. These humidifiers 41 and 42 are electrically connected to the control unit 45, respectively, and are configured so that the dew point can be adjusted by changing the temperature of the water according to a command from the control unit 45.

The current measuring device 43 is arranged, for example, in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 of the cell 1, measures the current in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32, and displays the measurement result. It is transmitted to the control unit 45. On the other hand, the current measuring device 44 is arranged, for example, in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35 of the cell 1, measures the current in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35, and measures the current. The result is transmitted to the control unit 45.

The control unit 45 includes, for example, a CPU (Central Processing Unit) that executes an operation, a ROM (Read only memory) as a secondary storage device that stores a program for the operation, a storage of the operation progress, and a temporary control. It is configured by a microcomputer that is combined with a RAM (Random access memory) as a temporary storage device that stores variables, and executes the stored programs to control each component forming the aging device 40.

For example, the control unit 45 adjusts the dew point (that is, the humidified state) of the humidifiers 41 and 42 based on the measurement results of the current measuring devices 43 and 44. More specifically, the control unit 45 controls the current measurement values in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 transmitted by the current measuring device 43, the fuel gas outlet 34 transmitted by the current measuring device 44, and Compared with the current measurement values in the vicinity of the oxidant gas outlet 35, the current measurement values in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 are obtained from the current measurement values in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35. When is also large, a control command for lowering the temperature is transmitted to the humidifiers 41 and 42 so as to reduce the humidity of the fuel gas and the oxidant gas to be humidified.

On the other hand, when the measured current values in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 are smaller than the measured current values in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35, the control unit 45 controls the fuel to be humidified. A control command for increasing the temperature is transmitted to the humidifiers 41 and 42 so as to increase the humidity of the gas and the oxidizing gas.

Further, as shown in FIG. 3, the aging device 40 further includes a discharger 46 for discharging the fuel cell 10 and a voltage measuring device 47 for measuring the voltage of the fuel cell 10.

FIG. 4 is a flow chart showing the aging method of the fuel cell according to the embodiment. When performing the fuel cell aging method using the above-described aging device 40, for example, first, the temperature of the water in the humidifiers 41 and 42 is set to 80° C., and the fuel gas and the oxidant gas are each humidified, and then the fuel cell 10 (Step S1). In order to control the temperature of the water more strictly, a heater or the like capable of adjusting the temperature may be further attached to the fuel gas supply pipe 11a and the oxidant gas supply pipe 12a, and the heating state of the heater or the like is controlled to supply the water. The temperature of the fuel gas and the oxidant gas flowing in the pipe can be adjusted.

Next, using the current measuring devices 43 and 44, the generated current near the fuel gas inlet 31 and the oxidant gas inlet 32 and the generated current near the fuel gas outlet 34 and the oxidant gas outlet 35 are measured, respectively. Yes (step S2). The control unit 45 acquires the measured values of the generated currents from the current measuring devices 43 and 44, and the measured current values near the fuel gas inlet 31 and the oxidant gas inlet 32 are the fuel gas outlet 34 and the oxidant gas outlet 35. It is determined whether or not it is larger than the current measurement value in the vicinity (step S3). When it is determined that the measured current values near the fuel gas inlet 31 and the oxidant gas inlet 32 are larger than the measured current values near the fuel gas outlet 34 and the oxidant gas outlet 35, the control unit 45 determines that the humidification is performed. A control command for lowering the temperature is transmitted to the humidifiers 41 and 42 so as to reduce the humidity of the fuel gas and the oxidant gas (step S4).

At this time, the humidifiers 41 and 42 receive the above-mentioned control command and lower the temperature of water. As shown in FIG. 5(A), when the temperature of the water in the humidifiers 41, 42 decreases (in other words, the dew point decreases), the water content in the fuel gas and the oxidant gas decreases, so the fuel gas inlet 31 Also, the wet state of the electrolyte membrane near the oxidant gas inlet 32 is lowered, and the conductivity of the electrolyte membrane is lowered. As a result, the electrochemical reaction in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 becomes relatively slow, and the generated current also decreases.

When the electrochemical reaction in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 becomes slow, the consumption of the reaction gas in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 is reduced, so that the fuel gas outlet 34 and the oxidant gas are oxidized. The concentration of the reaction gas toward the agent gas outlet 35 is maintained. Further, the water produced by the electrochemical reaction gradually improves the wet state of the electrolyte membrane as it approaches the fuel gas outlet 34 and the oxidant gas outlet 35 (in other words, the conductivity of the electrolyte membrane increases). , The generated current will gradually increase. In particular, in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35, the concentration of the reaction gas is maintained to some extent and the electrolyte membrane has the best wet state, so that the electrochemical reaction becomes relatively active.

Then, when step S4 ends, the generated current is measured again (step S2).

On the other hand, if it is determined in step S3 that the measured current values near the fuel gas inlet 31 and the oxidant gas inlet 32 are not greater than the measured current values near the fuel gas outlet 34 and the oxidant gas outlet 35, the control unit 45 Further determines whether the measured current values near the fuel gas inlet 31 and the oxidant gas inlet 32 are smaller than the measured current values near the fuel gas outlet 34 and the oxidant gas outlet 35 (step S5). When it is determined that the current measurement values near the fuel gas inlet 31 and the oxidant gas inlet 32 are smaller than the current measurement values near the fuel gas outlet 34 and the oxidant gas outlet 35, the control unit 45 determines that the humidification is performed. A control command for raising the temperature is transmitted to the humidifiers 41 and 42 so as to increase the humidity of the fuel gas and the oxidant gas (step S6).

At this time, the humidifiers 41 and 42 raise the temperature of water in response to the above-mentioned control command. When the temperature of the water in the humidifiers 41, 42 rises (in other words, the dew point rises), the water content in the fuel gas and the oxidant gas increases, so the electrolyte in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 The wet state of the membrane is improved, and the conductivity of the electrolyte membrane is increased. Therefore, the electrochemical reaction in the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 becomes relatively active, and the power generation current also rises. Along with this, the consumption of the reaction gas increases near the fuel gas inlet 31 and the oxidant gas inlet 32, and the concentration of the reaction gas toward the fuel gas outlet 34 and the oxidant gas outlet 35 decreases. The electrochemical reaction in the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35 becomes relatively slow, and the generated current also becomes low.

Then, when step S6 ends, the generated current is measured again (step S2).

On the other hand, when it is determined in step S5 that the current measurement values near the fuel gas inlet 31 and the oxidant gas inlet 32 are not smaller than the current measurement values near the fuel gas outlet 34 and the oxidant gas outlet 35 (that is, the fuel If the current measured values near the gas inlet 31 and the oxidant gas inlet 32 are equal to the current measured values near the fuel gas outlet 34 and the oxidant gas outlet 35), the temperature of the humidifier is maintained as it is, and the above step S1 is performed. Is done again.

In the fuel cell aging method according to the present embodiment, the power generation currents near the fuel gas inlet 31 and the oxidant gas inlet 32, and the power generation currents near the fuel gas outlet 34 and the oxidant gas outlet 35 are measured, respectively. 31 and the oxidant gas inlet 32 near the measured value of the generated current is larger than the measured value of the generated current at the fuel gas outlet 34 and the oxidant gas outlet 35, the humidity of the fuel gas and the oxidant gas to be humidified is reduced. A fuel gas and an oxidant gas that are humidified when the measured values of the generated current near the fuel gas inlet 31 and the oxidant gas inlet 32 are smaller than the measured values of the generated current near the fuel gas outlet 34 and the oxidant gas outlet 35, Since the humidity of the cell is increased, the wet state of the electrolyte membrane 5 (that is, the conductivity of the electrolyte membrane 5) and the concentration distributions of the fuel gas and the oxidant gas are adjusted, thereby biasing the current distribution of the entire cell. Can be suppressed. As a result, the current distribution of the entire cell can be kept uniform (for example, within 5%), and the aging time can be shortened.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. You can make changes. For example, in the above-described embodiment, the measurement position of the generated current has been described with reference to the vicinity of the fuel gas inlet 31 and the oxidant gas inlet 32 and the vicinity of the fuel gas outlet 34 and the oxidant gas outlet 35. The measurement positions may be further increased to obtain the distribution.

1 cell 2 MEGA
3 separator 4 membrane electrode assembly 5 electrolyte membrane 6 electrode 7 gas diffusion layer 8 gasket 10 fuel cell 21 fuel gas channel 22 oxidant gas channel 23 cooling water channel 31 fuel gas inlet 32 oxidant gas inlet 33 cooling water inlet 34 Fuel gas outlet 35 Oxidant gas outlet 36 Cooling water outlet 40 Aging devices 41, 42 Humidifiers 43, 44 Current measuring device 45 Control unit 46 Discharger 47 Voltage measuring device

Claims (1)

A fuel cell aging method for supplying a humidified reaction gas to perform aging for a fuel cell in which a plurality of cells having a reaction gas inlet and a reaction gas outlet are stacked,
At least measuring the generated current near the reaction gas inlet and near the reaction gas outlet,
When the measured value of the generated current near the reaction gas inlet is larger than the measured value of the generated current near the reaction gas outlet, the humidity of the humidified reaction gas is lowered, and the generated current near the reaction gas inlet is measured. A method for aging a fuel cell, comprising increasing the humidity of a reaction gas to be humidified when the value is smaller than the measured value of the generated current near the reaction gas outlet.

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